To lubricate a drive portion such as a motor shaft, refrigerating machine oil is sealingly filled in a compressor of an air-conditioning apparatus. When refrigerant in a wet vapor state is sucked into the compressor at the time of starting the compressor, or when a stagnation state in which refrigerant dissolves in the refrigerating machine oil is reached while the compressor is not operating, the refrigerating machine oil is mixed with the refrigerant, and is diluted as a result. When the operation of the air-conditioning apparatus is continued for a long period of time under a state in which a concentration of the oil is at a low level, the motor shaft and the like are not sufficiently lubricated. Thus, there is a fear that wear or burning may occur, resulting in a failure. Under a normal state, when the air-conditioning apparatus operates for a while after being started, the compressor is heated, and the refrigerant mixed with the refrigerating machine oil evaporates to be discharged. Thus, an oil concentration required for the operation is maintained.
There is known a technology in which a concentration of refrigerating machine oil inside a compressor is detected and the operation of the compressor is controlled appropriately depending on the detected concentration (see, for example, Patent Literature 1).